Use what works for you. That being said, I like the philly shell, because you only need one hand and your shoulder to block. The sideways stance is good for quick movement in and out. In kickboxing, it's harder to make work because you can't check leg kicks quite as well, but you can move out of the way, or even better, you can move in and stuff the kick before it develops full power and counter. In MMA, you can stuff the double from there, in fact, it's easier, because he's already eating your hips. But singles become harder to defend.

I am speaking from experience. But don't take my word for it. In Sanshou, the sideways, Philly Shell stance is known as the Chinses stance. In his book, Cung Le discusses the strengths and weakness of the Chinse stance on page 15. Here are his exact words painstakingly typed out...

Use what works for you. That being said, I like the philly shell, because you only need one hand and your shoulder to block. The sideways stance is good for quick movement in and out. In kickboxing, it's harder to make work because you can't check leg kicks quite as well, but you can move out of the way, or even better, you can move in and stuff the kick before it develops full power and counter. In MMA, you can stuff the double from there, in fact, it's easier, because he's already eating your hips. But singles become harder to defend.

Sanshou: The Complete Fighting System by Cung Le pages 14-15

Standard Stance

"...The primary downfall with the standard stance is that due to your squared posture, you are susceptible to side kicks and double legs..."

"...the strengths of the standard stance are the weaknesses of the Chinese stance, and vice versa..."

As for everything that Cung doesn't talk about, everyone knows you can't really check kicks from the side stance. Ask any karateka, though, and they prefer the side stance to the forward stance to cover more distance. Covering more distance in the same amount of time is called BEING FASTER. And moving in to the punch is just a basic principle of boxing. He's aiming for where you were, not where you're going to be, so you step in, takes away all the power if you do it right. It's risky, but inside fighters do it all the time.

I am speaking from experience. But don't take my word for it. In Sanshou, the sideways, Philly Shell stance is known as the Chinses stance. In his book, Cung Le discusses the strengths and weakness of the Chinse stance on page 15. Here are his exact words painstakingly typed out...

As for everything that Cung doesn't talk about, everyone knows you can't really check kicks from the side stance. Ask any karateka, though, and they prefer the side stance to the forward stance to cover more distance. Covering more distance in the same amount of time is called BEING FASTER. And moving in to the punch is just a basic principle of boxing. He's aiming for where you were, not where you're going to be, so you step in, takes away all the power if you do it right. It's risky, but inside fighters do it all the time.

Whatever, you'd still troll me if I didn't quote Cung Le. Look, I agree with Cung Le's theories based on my own experience as a karateka and as a wrestler. What exactly are you disagreeing with me here on?

I know this is some serious thread necro but I was without internet for weeks.

I am more likely to employ it when I possess a combination of superior: height and/or reach and/or experience and/or speed.

The less I have those, the more likely I'll employ a more traditional, textbook boxing guard. This doesn't just apply to crab, but to any and all possible hand configurations that would have my left hand down (I'm orthodox).

If I'm going to deliberately use it when it wouldn't be optimal, it's because I'm trying to practice counters after slipping/ducking. That's not to say I couldn't do that with a more traditional guard but.. yeah.